Imagine hearing a distant roll of thunder and wondering what caused it. Even asking that question is a sign that you, like all humans, can perform a type of sophisticated thinking known as “causal reasoning”—inferring that mechanisms you can’t see may be responsible for something. But humans aren’t alone in this ability: New Caledonian crows can also reason about hidden mechanisms, or “causal agents,” a team of scientists report Sept. 17 in the Proceedings of the National Academy of Sciences. It’s the first time that this cognitive ability has been experimentally demonstrated in a species other than humans, and the method may help scientists understand how this type of reasoning evolved, the researchers say.